Radio Digest (July 1924-Apr 1925)

April 4, 1925 RADIO DIGES T— Illustrated 19 Audio Frequency Amplifier Tube Couplings Combinations Are Often Desirable By William Alexander WHEN designing: a set the reader has the choice of many different varieties of Radio frequency amplification; as it is done in the Neutrodyne, the Hetduogen, super-heterodyne or tuned range. Very little space has been devoted in most of the Radio periodicals to amplification of signals after they have passed the rectifying detector and are direct current pulsations. ' Figure 1 Figure Radio frequency. During the past Radio season most of the attention has been paid to Radio frequency amplification, to increase selectivity and gain greater The writer proposes to present several methods of audio frequency amplification, and combinations of those methods, as the combination which works well on one The Maker's Name — A Public Promise '"ORISTOL" on the new Bristol's Loud Speakers indicates JD established responsibility and safeguards the buyer who knows the name. Technical engineers know that for 36 years The Bristol Company has made for the great plants of America, highly accurate and sensitive Recording Instruments, and that they are fully qualified to make loud speakers of great excellence. They know that Bristol experience, scientific knowledge and honest purpose, must be this loud speaker's full inheritance. Cabinet Model, $30.00 There are five loud speakers, but all alike in those essentials, which give true quality to the reproduction of voice or instrumental music. The "Voice" is not a mere phone unit, but an electromagnetic device, and the horns of non-metallic material with long sound chambers allow free and full vibration. Prices $12.50 to $30.00. If not at your dealer's, send for Bulletin AY-3022. set is not always the most efficient on another. The system most commonly used is that of transformer coupling, with resistance coupling rapidly gaining in popularity. Push pull amplification, while a variety of transformer coupling, is used exclusively as the last stage of an audio frequency amplifier and may be used with either of the above mentioned systems. Signals in the plate circuit of the detector tube consist of direct current pulsations varying in frequency from 16 to about 15,000 per second. If these pulsa Transformer Coupling* Taking up transformer coupling first, we find that the chief unit used is the audio frequency transformer. This consists of a core made up of either flat strips of iron or iron wire on which is wound several layers of fine wire, known as the primary, because the energy is put into this winding. The secondary, from which the energy is taken, also consists of many layers of fine wire, the number of turns depending on the ratio desired. This ratio of turns between secondary and Figure 3 tions are passed into a pair of head receivers they will be clearly heard, but will be comparatively faint. Strengthening of this energy is desirable, so that it will operate a loud speaker, and audio frequency amplification is the means resorted to for raising the strength of the energy sufficiently to operate a speaker. primary is usually anywhere from 2 to 1 up to 6 to 1. A steady uni-directional current flows from the B battery, keeping the plate of the detector tube at a constant positive voltage in relation to the filament. Since only the changes or variations in a current are passed by a trans(Continued on page 20) MACNATRON TT7HEN you use MAGNATRONS you * * are using vacuum tubes which have won the unqualified endorsement of radio fans and radio engineers alike. Tubes DO make a difference — as you'll discover the minute you equip with MAGNATRONS. The DC-201A, the DC-199, and the DC-199 with large hase, now list for only $3. Your dealer has them! COfWEWEY &£CTRfC lABORATOfiCeS 309 Fifth Avenue NEV YORK CITY Model "S" Audio phone $25.00 Horn 14%" diameter. Velvet mat finish o f bronze and gold. Classic base. BRISTOL^^Loud Speaker The BRISTOL COMPANY, Waterbury, Conn. POWER NOISES ELIMINATED Read This Gents: Jan. 7, 1925. We are so tickled with the results of the new Antennae, I must write you. Tou can imagine how appreciative we must be, after trying for a year, and all the Experts (?) of several cities failed, • to order a simple looking affair like your product and to get results, tor $20, is gratifying, surely. We used a machine with it, and must say most all stations worked perfectly no more of that awful stamp mill pounding and rattling. We had a handy layout, so we could slip off counterpoise wire and slip on ground. Immediately we put on ground a most awful interference came in, but just as soon as we switched back to counterpoise everything lovely. We placed in exact position you marked, etc. Any references you want to send to Elks Club, care of me, do so, and I will give you some boost. Every fan in town is up on building today, copying the layout for themselves. (Signed) DK. J. C. SMITH, Merced, Calif. Why Continue to Suffer from Power Interference? You can get the same relief from power noises as Dr. Smith did with the Kane Antennae, and for $13 instead of $20 under our new direct from factory to user system of selling. Our new policy — only one profit instead of three — sold direct from factory to user. Price «|> D»t>U 13.00 The Special Kane Antennae for Radiola Super-Hets. The Regular Kane Antennae for all Receiving' Sets Other than RCA Super-Hets and for Super-Hets Using a Booster. Price Postpaid to Any Part of the U. S. Shipped C. 0. D. when 25 per cent of price accompanies order. THE SENSATION OF THE PACIFIC COAST You see them everywhere from British Columbia to the Mexican Boundary. Full Working' Drawings of the Kane Antennae D * _ <£ / stamps With Complete Instructions for Erecting if ICC «Jpl Accep Not Accepted The Kane Antennae has linked the Atlantic and Pacific Coasts together by eliminating all power noises from broadcast reception. THE KANE ANTENNAE COMPANY Aberdeen, Washington